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By Authority Of 

THE UNITED STATES OF AMERICA 

Legally Binding Document 



By the Authority Vested By Part 5 of the United States Code § 552(a) and 
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INCORPORATED BY REFERENCE and shall be considered legally 
binding upon all citizens and residents of the United States of America. 
HEED THIS NOTICE : Criminal penalties may apply for noncompliance. 




Document Name: APHA Method 4500-CN: Standard Methods for the 

Examination of Water and Wastewater 

CFR Section(s): 40 CFR 136.3(a) 

Standards Body: American Public Health Association 



Standard 

For the 

Examination of 
Water and 
Wastewater 



: mm 



Imm^mmmm^mmm^ 



Prepared and published jointly by: 

American Public Health Association 

American Water Works Association 

Water Environment Federation 



joint Editorial Board 

Arnold E. Greenberg, APHA, Chairman 

Lenore S. Qesceri, WEF 

Andrew D. Eaton, AWWA 

Managing Editor 
Mary Ann H. Franson 

Publication Office 

American Public Health Association 

1015 Fifteenth Street, NW 
Washington, DC 20005 



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American Public Health Association. 

Standard methods for the examination of water and wastewater. 
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4-18 



INORGANIC NONMETALS (4000) 




4500-CN" CYANIDE* 



4500-CN" A. Introduction 



1. General Discussion 

^Cyanide 1 ' refers to all of the CN groups in cyanide compounds 
that can be determined as the cyanide ion, CN~ , by the methods 
used. The cyanide compounds in which cyanide can be obtained 
as CN" are classed as simple and complex cyanides. 

Simple cyanides are represented by the formula A(CN) X , where 
A is an alkali (sodium, potassium, ammonium) or a metal, and 
x, the valence of A, is the number of CN groups. In aqueous 
solutions of simple alkali cyanides, the CN group is present as 
CN~ and molecular HCN, the ratio depending on pH and the 
dissociation constant for molecular HCN (pK„ — 9.2). In most 
natural waters HCN greatly predominates. ' In solutions of simple 
metal cyanides, the CN group may occur also in the form of 
complex metal-cyanide anions of varying stability. Many simple 
metal cyanides are sparingly soluble or almost insoluble [CuCN, 
AgCN, Zn(CN) 2 ], but they form a variety of highly soluble, 
complex metal cyanides in the presence of alkali cyanides. 

Complex cyanides have a variety of formulae, but the alkali- 
metallic cyanides normally can be represented by A y M(CN) x . In 
this formula, A represents the alkali present y times, M the heavy 
metal (ferrous and ferric iron, cadmium, copper, nickel, silver, 



Approved by Standard Methods Committee. 1990. 



zinc, or others), and x the number of CN groups; x is equal to 
the valence of A taken y times plus that of the heavy metal. 
Initial dissociation of each of these soluble, alkali-metallic, com- 
plex cyanides yields an anion that is the radical M(CN)/~. This 
may dissociate further, depending on several factors, with the 
liberation of CN" and consequent formation of HCN. 

The great toxicity to aquatic life of molecular HCN is well 
known; 2 " 5 it is formed in solutions of cyanide by hydrolytic re- 
action of CN™ with water. The toxicity of CN" is less than that 
of HCN; it usually is unimportant because most of the free cy- 
anide (CN group present as CN~ or as HCN) exists as HCN, 25 
as the pH of most natural waters is substantially lower than the 
pK„ for molecular HCN. The toxicity to fish of most tested so- 
lutions of complex cyanides is attributable mainly to the HCN 
resulting from dissociation of the complexes. 24 - 5 Analytical dis- 
tinction between HCN and other cyanide species in solutions of 
complex cyanides is possible, 25 ™ 910 

The degree of dissociation of the various metallocyanide com- 
plexes at equilibrium, which may not be attained for a long time, 
increases with decreased concentration and decreased pH, and 
is inversely related to their highly variable stability. 2 - 4 - 5 The zinc- 
and cadmium-cyanide complexes are dissociated almost totally 
in very dilute solutions; thus these complexes can result in acute 
toxicity to fish at any ordinary pH. In equally dilute solutions 



CYANIDE (4500-CN ^/Introduction 



4-19 



there is much less dissociation for the nickel-cyanide complex 
and the more stable cyanide complexes formed with copper (I) 
and silver. Acute toxicity to fish of dilute solutions containing 
copper-cyanide or silver-cyanide complex anions can be due mainly 
or entirely to the toxicity of the undissociated ions, although the 
complex ions are much less toxic than HCN. 25 

The iron-cyanide complex ions are very stable and not ma- 
terially toxic; in the dark, acutely toxic levels of HCN are attained 
only in solutions that are not very dilute and have been aged for 
a long time. However, these complexes are subject to extensive 
and rapid photolysis, yielding toxic HCN, on exposure of dilute 
solutions to direct sunlight. :u The photodecomposition depends 
on exposure to ultraviolet radiation, and therefore is slow in 
deep, turbid, or shaded receiving waters. Loss of HCN to the 
atmosphere and its bacterial and chemical destruction concurrent 
with its production tend to prevent increases of HCN concen- 
trations to harmful levels. Regulatory distinction between cya- 
nide complexed with iron and that bound in less stable com- 
plexes, as well as between the complexed cyanide and free cyanide 
or HCN, can, therefore, be justified. 

Historically, the generally accepted physicochemical technique 
for industrial waste treatment of cyanide compounds is alkaline 
chlorination: 



NaCN + CU -> CNC1 + NaCl 



(0 



The first reaction product on chlorination is cyanogen chloride 
(CNCl), a highly toxic gas of limited solubility. The toxicity of 
CNC1 may exceed that of equal concentrations of cyanide. 2 - 3 - 12 
At an alkaline pH, CNCl hydrolyzes to the cyanate ion (CNO), 
which has only limited toxicity. 

There is no known natural reduction reaction that may convert 
CNO to CN~. 13 On the other hand, breakdown of toxic CNCl 
is pH- and time-dependent. At pH 9, with no excess chlorine 
present, CNCl may persist for 24 h. 14 - 15 



CNCl + 2NaOH -> NaCNO + NaCl + H,0 



(2) 



CNO~ can be oxidized further with chlorine at a nearly neutral 
pH to C0 2 -andN 2 : 

2NaCNO + 4NaOH + 3CU -> 6NaCI + 2C0 2 + N 2 + 2HX> (3) 

CNO" also will be converted on acidification to NH 4 h : 

2NaCNO + H 2 S0 4 + 4H.O -► (NH 4 ) : S0 4 + 2NaHC0 3 (4) 

The alkaline chlorination of cyanide compounds is relatively 
fast, but depends equally on the dissociation constant, which also 
governs toxicity. Metal cyanide complexes, such as nickel, cobalt, 
silver, and gold, do not dissociate readily. The chlorination re- 
action therefore requires more time and a significant chlorine 
excess. 16 Iron cyanides, because they do not dissociate to any 
degree, are not oxidized by chlorination. There is correlation 
between the refractory properties of the noted complexes, in 
their resistance to chlorination and lack of toxicity. 

Thus, it is advantageous to differentiate between total cyanide 
and cyanides amenable to chlorination. When total cyanide is 
determined, the almost nondissociable cyanides, as well as cy- 
anide bound in complexes that are readily dissociable and com- 
plexes of intermediate stability, are measured. Cyanide com- 



pounds that are amenable to chlorination include free cyanide 
as well as those complex cyanides that are potentially dissociable, 
almost wholly or in large degree, and therefore, potentially toxic 
at low concentrations, even in the dark. The chlorination test 
procedure is carried out under rigorous conditions appropriate 
for measurement of the more dissociable forms of cyanide. 

The free and potentially dissociable cyanides also may be es- 
timated when using the weak acid dissociable procedure. These 
methods depend on a rigorous distillation, but the solution is 
only slightly acidified, and elimination of iron cyanides is insured 
by the earlier addition of precipitation chemicals to the distil- 
lation flask or by the avoidance of ultraviolet irradiation. 

The cyanogen chloride procedure is common with the colori- 
metric test for cyanides amenable to chlorination. This test is 
based on the addition of chloramine-T and subsequent color 
complex formation with barbituric acid. Without the addition of 
chloramine-T, only existing CNCl is measured. CNCl is a gas 
that hydrolyzes to CNO'; sample preservation is not possible. 
Because of this, spot testing of CNCl levels may be best. This 
procedure can be adapted and used when the sample is collected. 

There may be analytical requirements for the determination 
of CNO", even though the reported toxicity level is low. On 
acidification, CNO" decomposes to ammonia (NH 3 ). 3 Molecular 
ammonia and metal-ammonia complexes are toxic to aquatic 
life. 17 

Thiocyanate (SCN~) is not very toxic to aquatic life. 218 How- 
ever, upon chlorination, toxic CNCl is formed, as discussed 
above. 2 - 3 - 12 At least where subsequent chlorination is anticipated, 
the determination of SCN" is desirable. Thiocyanate is biode- 
gradable; ammonium is released in this reaction. Although the 
typical detoxifying agents used in cyanide poisoning induce thi- 
ocyanate formation, biochemical cyclic reactions with cyanide 
are possible, resulting in detectable levels of cyanide from ex- 
posure to thiocyanate. 18 Thiocyanate may be analyzed in samples 
properly preserved for determination of cyanide; however, thi- 
ocyanate also can be preserved in samples by acidification with 
H 2 S0 4 to pH <2. 



2. Cyanide in Solid Waste 

a. Soluble cyanide: Determination of soluble cyanide requires 
sample leaching with distilled water until solubility equilibrium 
is established. One hour of stirring in distilled water should be 
satisfactory. Cyanide analysis is then performed on the leachate. 
Low cyanide concentration in the leachate may indicate presence 
of sparingly soluble metal cyanides. The cyanide content of the 
leachate is indicative of residual solubility of insoluble metal 
cyanides in the waste. 

High levels of cyanide in the leachate indicate soluble cyanide 
in the solid waste. When 500 mL distilled water are stirred into 
a 500-mg solid waste sample, the cyanide concentration (mg/L) 
of the leachate multiplied by 1000 will give the solubility level 
of the cyanide in the solid waste in milligrams per kilogram. The 
leachate may be analyzed for total cyanide and/or cyanide ame- 
nable to chlorination. 

b. Insoluble cyanide: The insoluble cyanide of the solid waste 
can be determined with the total cyanide method by placing a 
500-mg sample with 500 mL distilled water in the distillation 
flask and in general following the distillation procedure (Section 
4500-CN" .C). In calculating, multiply by 1000 to give the cyanide 



4-20 



INORGANIC NONMETALS (4000) 



content of the solid sample in milligrams per kilogram. Insoluble 
iron cyanides in the solid can be leached out earlier by stirring 
a weighed sample for 12 to 16 h in a 10% NaOH solution. The 
leached and wash waters of the solid waste will give the iron 
cyanide content with the distillation procedure. Prechlorination 
will have eliminated all cyanide amenable to chlorination. Do 
not expose sample to sunlight. 



3. Selection of Method 

a. Total cyanide after distillation: After removal of interfering 
substances, the metal cyanide is converted to HCN gas, which 
is distilled and absorbed in sodium hydroxide (NaOH) solution. ,y 
Because of the catalytic decomposition of cyanide in the presence 
of cobalt at high temperature in a strong acid solution, 20 - 21 co- 
balticyanide is not recovered completely. Indications are that 
cyanide complexes of the noble metals, i.e., gold, platinum, and 
palladium, are not recovered fully by this procedure either. Dis- 
tillation also separates cyanide from other color-producing and 
possibly interfering organic or inorganic contaminants. Subse- 
quent analysis is for the simple salt, sodium cyanide (NaCN). 
Some organic cyanide compounds, such as cyanohydrins, are 
decomposed by the distillation. Aldehydes convert cyanide to 
cyanohydrins. 

The absorption liquid is analyzed by a titrimetric, colorimetric, 
or cyanide-ion-selective electrode procedure: 

1) The titration method (D) is suitable for cyanide concentra- 
tions above 1 mg/L. 

2) The colorimetric method (E) is suitable for cyanide con- 
centrations to a lower limit of 5 to 20 |mg/L. Analyze higher 
concentrations by diluting either the sample before distillation 
or the absorber solution before colorimetric measurement. 

3) The ion-selective electrode method (F) using the cyanide 
ion electrode is applicable in the concentration range of 0.05 to 
10 mg/L. 

b. Cyanide amenable to chlorination: 

1) Distillation of two samples is required, one that has been 
chlorinated to destroy all amenable cyanide present and the other 
unchlorinated. Analyze absorption liquids from both tests for 
total cyanide. The observed difference equals cyanides amenable 
to chlorination. 

2) The colorimetric method, by conversion of amenable cya- 
nide and SCN to CNCl and developing the color complex with 
barbituric acid, is used for the determination of the total of these 
cyanides (H). Repeating the test with the cyanide masked by the 
addition of formaldehyde provides a measure of the SCN ~ con- 
tent. When subtracted from the earlier results this provides an 
estimate of the amenable CN content. This method is useful 
for natural and ground waters, clean metal finishing, and heat 
treating effluents. Sanitary wastes may exhibit interference. 

3) The weak acid dissociable cyanides procedure also measures 
the cyanide amenable to chlorination by freeing HCN from the 
dissociable cyanide. After being collected in a NaOH absorption 
solution, CN~ may be determined by one of the three finishing 
procedures given for the total cyanide determination. 

It should be noted that although cyanide amenable to chlo- 
rination and weak acid dissociable cyanide appear to be identical, 
certain industrial effluents (e.g., pulp and paper, petroleum re- 
fining industry effluents) contain some poorly understood sub- 
stances that may produce interference. Application of the pro- 



cedure for cyanide amenable to chlorination yields negative values. 
For natural waters and metal-finishing effluents, the direct col- 
orimetric determination appears to be the simplest and most 
economical. 

c. Cyanogen chloride: The colorimetric method for measuring 
cyanide amenable to chlorination may be used, but omit the 
chloramine-T addition. The spot test also may be used. 

d. Spot test for sample screening: This procedure allows a quick 
sample screening to establish whether more than 50 jmg/L cyanide 
amenable to chlorination is present. The test also may be used 
to estimate the CNCI content at the time of sampling. 

e. Cyanate: CNO - is converted to ammonium carbonate, 
(NH 4 ) 2 C0 3 , by acid hydrolysis at elevated temperature. Am- 
monia (NH 3 ) is determined before the conversion of the CNO 
and again afterwards. The CNO" is estimated from the differ- 
ence in NH 3 found in the two tests. 22 " 24 Measure NH 3 by either: 

1) The selective electrode method, using the NH 3 gas elec- 
trode; or 

2) The colorimetric method, using direct nesslerization or the 
phenate method for NH 3 (Section 4500-NH 3 .C or D). 

/. Thiocyanate: Use the colorimetric determination with ferric 
nitrate as a color-producing compound. 



4. References 

1. Milne, D. 1950. Equilibria in dilute cyanide waste solutions. Sewage 
Ind. Wastes 23:904. 

2. Doudoroff, P. J 976. Toxicity to fish of cyanides and related com- 
pounds. A review. EPA 600/3-76-038, U.S. Environmental Protec- 
tion Agency, Duluth, Minn. 

3. Doc dor off, P. & M. Katz. 1950. Critical review of literature on 
the toxicity of industrial wastes and their components to fish. Sewage 
but. Wastes 22:1432. 

4. Doudoroff, P. 1956. Some experiments on the toxicity of complex 
cyanides to fish. Sewage Ind. Wastes 28:1020. 

5. Doudoroff, P., G. Leduc & C.R. Schneider. 1966. Acute toxicity 
to fish of solutions containing complex metal cyanides, in relation 
to concentrations of molecular hydrocyanic acid. Trans. Amer. Fish. 
Soc. 95:6. 

6. Schneider, C.R. & H. Freund. 1962. Determination of low level 
hydrocyanic acid. Anal. Chem. 34:69. 

7. Claeys R. & H. Freund. 1968. Gas chromatographic separation of 
HCN. Environ. Set. Technol. 2:458. 

8. Montgomery, H.A.C., D.K. Gardiner & J.G. Gregory. 1969. 
Determination of free hydrogen cyanide in river water by a solvent- 
extraction method. Analyst 94:284. 

9. Nelson, K.H. & L. Lysyx 1971. Analysis of water for molecular 
hydrogen cyanide. ./. Water Pollut. Control Fed. 43:799. 

10. Broderius, S.J. 1981. Determination of hydrocyanic acid and free 
cyanide in aqueous solution. Anal. Chem. 53:1472. 

1 1 . Burdick, G.E. & M. Lipschuetz. 1948. Toxicity of ferro and fer- 
ricyanide solutions to fish. Trans. Amer. Fish. Soc. 78:192. 

12. Zillich, J.A. 1972. Toxicity of combined chlorine residuals to fresh- 
water fish. J. Water Polka. Control Fed. 44:212. 

13. Resnick, J.D., W. Moore & M.E. Ettinger. 1958. The behavior 
of cyanates in polluted waters. Ind. Eng. Chem. 50:71. 

14. Pettet, A.E.J. & G.C. Ware. 1955. Disposal of cyanide wastes. 
Chem. Ind. 1955:1232. 

.15. Bailey, P.L. & E, Bishop. 1972. Hydrolysis of cyanogen chloride. 
Analyst 97:691. 

16. Lancy, L. & W. Zabban. 1962. Analytical methods and instru- 
mentation for determining cyanogen compounds. Spec. Tech. Publ. 
337, American Soc. Testing & Materials, Philadelphia, Pa. 



CYANIDE (4500-CN ")/Sample Pretreatment 



4-21 



17. CalamarkD. &R. Marchetti. 1975. Predicted and observed acute 
toxicity of copper and ammonia to rainbow trout. Progr. Water Tech- 
no!. 7(3-4) :569. 

18. Wood, J.L. 1975. Biochemistry. Chapter 4 in A. A. Newman, ed. 
Chemistry and Biochemistry of Thiocyanic Acid and its Derivatives. 
Academic Press, New York, N.Y. 

19. Serfass, E.J. & R.B. Freeman. 1952. Analytical method for the 
determination of cyanides in plating wastes and in effluents from 
treatment processes. Plating 39:267. 

20. Leschber, R. & H. SCHLiomNG. 1969. Uber die Zersetzlichkeit 



Komplexer Metallcyanide bei der Cyanidbestimmung in Abwasser. 
Z. Anal. Chem. 245:300. 

21. Bassett, H., Jr. & A.S. Corbet. 1924. The hydrolysis of potassium 
ferricyanide and potassium cobalticyanide by sulfuric acid. ./. Chem. 
Soc. 125:1358. 

22. Dodge, B.F. & W. Zabban. 1952. Analytical methods for the de- 
termination of cyanates in plating wastes. Plating 39:381. 

23. Gardner, D.C. 1956. The colorimetric determination of cyanates 
in effuents. Plating 43:743. 

24. Procedures for Analyzing Metal Finishing Wastes. 1954. Ohio River 
Valley Sanitation Commission, Cincinnati, Ohio. 



4500-CN™ B. Preliminary Treatment of Samples 



Caution — Use care in manipulating cyanide-containing sam- 
ples because of toxicity. Process in a hood or other well-ventilated 
area. Avoid contact, inhalation, or ingestion. 

1 . General Discussion 

The nature of the preliminary treatment will vary according 
to the interfering substance present. Sulfides, fatty acids, and 
oxidizing agents are removed by special procedures. Most other 
interfering substances are removed by distillation. The impor- 
tance of the distillation procedure cannot be overemphasized. 

2. Preservation of Samples 

Oxidizing agents, such as chlorine, decompose most cyanides. 
Test by placing a drop of sample on a strip of potassium iodide 
(Kl)-starch paper previously moistened with acetate buffer so- 
lution, pH 4 (Section 4500-Cl.C.3e). If a bluish discoloration is 
noted, add 0. 1 g sodium arsenite (NaAs0 2 )/L sample and retest. 
Repeat addition if necessary. Sodium thiosulfate also may be 
used, but avoid an excess greater than 0.1 g Na 2 S 2 3 /L. Man- 
ganese dioxide, nitrosyl chloride, etc., if present, also may cause 
discoloration of the test paper. If possible, carry out this pro- 
cedure before preserving sample as described below. If the fol- 
lowing test indicates presence of sulfide, oxidizing compounds 
would not be expected. 

Oxidized products of sulfide convert CN " to SCN" rapidly, 
especially at high pH. 1 Test for S~ " by placing a drop of sample 
on lead acetate test paper previously moistened with acetic acid 
buffer solution, pH 4 (Section 4500-Cl.C.3e). Darkening of the 
paper indicates presence of S-~. Add lead acetate, or if the S 2 ~ 
concentration is too high, add powdered lead carbonate [Pb(C0 3 ) 2 ] 
to avoid significantly reducing pH. Repeat test until a drop of 
treated sample no longer darkens the acidified lead acetate test 
paper. Filter sample before raising pH for stabilization. When 
particulate, metal cyanide complexes are suspected, filter solu- 
tion before removing S 2 ". Reconstitute sample by returning fil- 
tered particulates to the sample bottle after S 2 ~ removal. Ho- 
mogenize particulates before analyses. 

Aldehydes convert cyanide to cyanohydrin. Longer contact 
times between cyanide and the aldehyde and the higher ratios 
of aldehyde to cyanide both result in increasing losses of cyanide 
that are not reversible during analysis. If the presence of alde- 
hydes is suspected, stabilize with NaOH at time of collection and 



add 2 mL 3.5% ethylenediamine solution per 100 mL of sample. 

Because most cyanides are very reactive and unstable, analyze 
samples as soon as possible. If sample cannot be analyzed im- 
mediately, add NaOH pellets or a strong NaOH solution to raise 
sample pH to 12 to 12.5 and store in a closed, dark bottle in a 
cool place. 

To analyze for CNC1 collect a separate sample and omit NaOH 
addition because CNC1 is converted rapidly to CNO" at high 
pH. Make colorimetric estimation immediately after sampling. 



3. Interferences 

a. Oxidizing agents may destroy most of the cyanide during 
storage and manipulation. Add NaAs0 2 or Na 2 S 2 3 as directed 
above; avoid excess Na 2 S 2 3 . 

b. Sulfide will distill over with cyanide and, therefore, ad- 
versely affect colorimetric, titrimetric, and electrode procedures. 
Test for and remove S 2 ~ as directed above. Treat 25 mL more 
than required for the distillation to provide sufficient filtrate 
volume. 

c. Fatty acids that distill and form soaps under alkaline titration 
conditions make the end point almost impossible to detect. Re- 
move fatty acids by extraction. 2 Acidify sample with acetic acid 
(1 + 9) to pH 6.0 to 7.0. (Caution — Perform this operation in 
a hood as quickly as possible.) Immediately extract with iso- 
octane, hexane, or CHC1 3 (preference in order named). Use a 
solvent volume equal to 20% of sample volume. One extraction 
usually is adequate to reduce fatty acid concentration below the 
interference level. Avoid multiple extractions or a long contact 
time at low pH to minimize loss of HCN. When extraction is 
completed, immediately raise pH to >12 with NaOH solution. 

d. Carbonate in high concentration may affect the distillation 
procedure by causing the violent release of carbon dioxide with 
excessive foaming when acid is added before distillation and by 
reducing pH of the absorption solution. Use calcium hydroxide 
to preserve such samples. 3 Add calcium hydroxide slowly, with 
stirring, to pH 12 to 12.5, After precipitate settles, decant su- 
pernatant liquid for determining cyanide. 

Insoluble complex cyanide compounds will not be determined. 
If such compounds are present, filter a measured amount of well- 
mixed treated sample through a glass fiber or membrane filter 
(47-mm diam or less). Rinse filter with dilute (1 to 9) acetic acid 
until effervescence ceases. Treat entire filter with insoluble ma- 



4-22 



INORGANIC NONMETALS (4000) 



terial as insoluble cyanide (4500-CN" .A.2/?) or add to filtrate 
before distillation. 

e. Other possible interferences include substances that might 
contribute color or turbidity. In most cases, distillation will re- 
move these. 

Note, however, that the strong acid distillation procedure re- 
quires using sulfuric acid with various reagents. With certain 
wastes, these conditions may result in reactions that otherwise 
would not occur in the aqueous sample. As a quality control 
measure, periodically conduct addition and recovery tests with 
industrial waste samples. 

/. Aldehydes convert cyanide to cyanohydrin, which forms ni- 
trile under the distillation conditions. Only direct titration with- 
out distillation can be used, which reveals only non-complex 
cyanides. Formaldehyde interference is noticeable in concen- 
trations exceeding 0.5 mg/L. Use the following spot test to es- 
tablish absence or presence of aldehydes (detection limit 0.05 
mg/L): 4 " 6 

1) Reagents 

a) MBTH indicator solution: Dissolve 0.05 g 3-methyl, 2-ben- 
zothiazolone hydrazone hydrochloride in 100 mL water. Filter 
if turbid. 

b) Ferric chloride oxidizing solution: Dissolve 1.6 g sulfamic 
acid and 1 g FeCl 3 -6H 2 in 100 mL water. 

c) Ethylenediamine solution, 3.5%: Dilute 3,5 mL pharma- 
ceutical-grade anhydrous NH 2 CH 2 CH 2 NH 2 to 100 mL with water. 

2). Procedure — If the sample is alkaline, add 1 + 1 H 2 S0 4 to 
10 mL sample to adjust pH to less than 8. Place 1 drop of sample 
and I drop distilled water for a blank in separate cavities of a 
white spot plate. Add 1 drop MBTH solution and then 1 drop 
FeCl 3 oxidizing solution to each spot. Allow 10 min for color 
development. The color change will be from a faint green-yellow 
to a deeper green with blue-green to blue at higher concentra- 
tions of aldehyde. The blank should remain yellow. 

To minimize aldehyde interference, add 2 mL of 3.5% eth- 
ylenediamine solution/100 mL sample. This quantity overcomes 
the interference caused by up to 50 mg/L formaldehyde. 

When using a known addition in testing, 100% recovery of 
the CN" is not necessarily to be expected. Recovery depends 
on the aldehyde excess, time of contact, and sample temperature. 

g. Glucose and other sugars, especially at the pH of preser- 
vation, lead to cyanohydrin formation by reaction of cyanide 
with aldose, 7 Reduce cyanohydrin to cyanide with ethylenedi- 
amine (see f above). MBTH is not applicable. 

h. Nitrite may form HCN during distillation in Methods C, G, 
and L, by reacting with organic compounds. K - y Also, N0 3 " may 
reduce to N0 2 , which interferes. To avoid N0 2 ~ interference, 
add 2 g sulfamic acid to the sample before distillation. Nitrate 
also may interfere by reacting with SCN~ .'" 

/. Some sulfur compounds may decompose during distillation, 
releasing S, H 2 S, or S0 2 . Sulfur compounds may convert cyanide 
to thiocyanate and also may interfere with the analytical pro- 
cedures for CN~ , To avoid this potential interference, add 50 
mg PbC0 3 to the absorption solution before distillation. Filter 
sample before proceeding with the colorimetric or titrimetric 
determination. 

Absorbed SO. forms Na^SCX which consumes chloramine-T 



added in the colorimetric determination. The volume of chlor- 
amine-T added is sufficient to overcome 100 to 200 mg S0 3 2 / 
L. Test for presence of chloramine-T after adding it by placing 
a drop of sample on Kl-starch test paper; add more chloramine- 
T if the test paper remains blank, or use Method F. 

Some wastewaters, such as those from coal gasification or 
chemical extraction mining, contain high concentrations of sul- 
fites. Pretreat sample to avoid overloading the absorption so- 
lution with S0 3 2 " . Titrate a suitable sample iodometrically (Sec- 
tion 4500-O) with dropwise addition of 30% H 2 2 solution to 
determine volume of FI 2 2 needed for the 500 mL distillation 
sample. Subsequently, add H 2 2 dropwise while stirring, but in 
only such volume that not more than 300 to 400 mg SO, 2 /L will 
remain. Adding a lesser quantity than calculated is required to 
avoid oxidizing any CN ~ that may be present. 

j. Alternate procedure: The strong acid distillation procedure 
uses concentrated acid with magnesium chloride to dissociate 
metal-cyanide complexes. In some instances, particularly with 
industrial wastes, it may be susceptible to interferences such as 
those from conversion of thiocyanate to cyanide in the presence 
of an oxidant, e.g., nitrate. If such interferences are present use 
a ligand displacement procedure with a mildly acidic medium 
with EDTA to dissociate metal-cyanide complexes. 10 Under such 
conditions thiocyanate is relatively stable and many oxidants, 
including nitrate, are weaker. 

If any cyanide procedure is revised to meet specific require- 
ments, obtain recovery data by the addition of known amounts 
of cyanide. 

4. References 

1. Luthy, R.G. & S. G. Bruce, Jr. 1979. Kinetics of reaction of 
cyanide and reduced sulfur species in aqueous solution. Environ. 
Sci. Techno! . 13:1481. 

2. Kruse, J.M. & M.G. Mellon. 1951. Colorimetric determination of 
cy a n i de s . Se wage In d. Wastes 23 : 1 402 . 

3. Luthy, R.G., S.G. Bruce, R.W. Walters & D.V. Nakles. 1979. 
Cyanide and thiocyanate in coal gasification wastewater. J. Water 
Pollut. Control Fed. 51:2267. 

4. Sawicki, E., T.W. Stanley, T.R. Hauser & W. Elbert. 1961. 
The 3-methyl-2-benzothiazoJone hydrazone test. Sensitive new 
methods for the detection, rapid estimation, and determination of 
aliphatic aldehydes. Anal. Chem. 33:93. 

5. Hauser, T.R. & R.L. Cummins. 1964. Increasing sensitivity of 3- 
methyi-2-benzothiazone hydrazone test for analysis of aliphatic al- 
dehydes in air. Anal. Chem. 36:679. 

6. Methods of Air Sampling and Analysis, 1st ed. 1972. Inter Society 
Committee, Air Pollution Control Assoc., pp. 199-204. 

7. Raaf,S.F.,W.G.Characklis,M.A. Kessick& C.H.Ward. 1977. 
Fate of cyanide and related compounds in aerobic microbial systems. 
Water Res. 11:477. 

8. Rapean, J.C., T. Hanson & R. A. Johnson. 1980. Biodegradation 
of cyanide-nitrate interference in the standard test for total cyanide. 
Proc. 35th Ind. Waste Conf., Purdue Univ.. Lafayette, Ind., p. 430. 

9. Casey, J. P. 1980. Nitrosation and cyanohydrin decomposition ar- 
tifacts in distillation test for cyanide. Extended Abs. American 
Chemical Soc, Div. Environmental Chemistry, Aug. 24-29, 1980. 
Las Vegas, Nev. 

10. Csikai, N.J. & A.J. Barnard, Jr. 1983. Determination of total 
cyanide in thiocyanate-containing waste water. Anal. Chem. 55: 1 677. 



CYANIDE (4500-CN )/Total CN after Distillation 



4-23 



4500-CN" C. Total Cyanide after Distillation 



1. General Discussion 



4. Procedure 



Hydrogen cyanide (HCN) is liberated from an acidified sample 
by distillation and purging with air. The HCN gas is collected 
by passing it through an NaOH scrubbing solution. Cyanide con- 
centration in the scrubbing solution is determined by titrimetric, 
colorimetric, or potentiometric procedures. 

2. Apparatus 

The apparatus is shown in Figure 4500-CN ~ :1. It includes: 

a. Boiling flask, 1 L, with inlet tube and provision for water- 
cooled condenser. 

b. Gas absorber, with gas dispersion tube equipped with 
medium-porosity fritted outlet. 

c. Heating element, adjustable. 

d. Ground glass ST joints, TFE-sIeeved or with an appropriate 
lubricant for the boiling flask and condenser. Neoprene stopper 
and plastic threaded joints also may be used. 

3. Reagents 

a. Sodium hydroxide solution: Dissolve 40 g NaOH in water 
and dilute to 1 L. 

b. Magnesium chloride reagent: Dissolve 510 g MgCl 2 -6H 2 
in water and dilute to 1 L. 

c. Sulfuric acid, H 2 S0 4 , 1 + 1. 

d. Lead carbonate, PbC0 3 , powdered. 

e. Sulfamic acid, NH 2 S0 3 H. 



Allihn 

Water- 

Cooled 

Condenser 



Thistle Tube 



Water In 



9- mm Connecting Tube 




Suction 



Heating 
Mantle 



38-mm X 200-mm 
Test Tube 



Figure 4500-CN :1. Cyanide distillation apparatus. 



a. Add 500 inL sample, containing not more than 10 mg CN"/ 
L (diluted if necessary with distilled water) to the boiling flask. 
If a higher CN" content is anticipated, use the spot test (4500- 
CN ~ .K) to approximate the required dilution. Add 10 mL NaOH 
solution to the gas scrubber and dilute, if necessary, with distilled 
water to obtain an adequate liquid depth in the absorber. Do 
not use more than 225 mL total volume of absorber solution. 
When S 2 ~ generation from the distilling flask is anticipated add 
50 or more mg powdered PbCO ? to the absorber solution to 
precipitate S 2 ". Connect the train, consisting of boiling flask air 
inlet, flask, condenser, gas washer, suction flask trap, and as- 
pirator. Adjust suction so that approximately 1 air bubble/s en- 
ters the boiling flask. This air rate will carry HCN gas from flask 
to absorber and usually will prevent a reverse flow of HCN 
through the air inlet. If this air rate does not prevent sample 
backup in the delivery tube, increase air-flow rate to 2 air bub- 
bles/s. Observe air purge rate in the absorber where the liquid 
level should be raised not more than 6.5 to 10 mm. Maintain air 
flow throughout the reaction. 

b. Add 2 g sulfamic acid through the air inlet tube and wash 
down with distilled water, 

c. Add 50 mL 1 i H 2 S0 4 through the air inlet tube. Rinse tube 
with distilled water and let air mix flask contents for 3 min. Add 
20 mL MgCl 2 reagent through air inlet and wash down with 
stream of water. A precipitate that may form redissolves on 
heating. 

d. Heat with rapid boiling, but do not flood condenser inlet 
or permit vapors to rise more than halfway into condenser. Ad- 
equate refluxing is indicated by a reflux rate of 40 to 50 drops/ 
min from the condenser lip. Reflux for at least 1 h. Discontinue 
heating but continue air flow for 15 min. Cool and quantitatively 
transfer absorption solution to a 250-mL volumetric flask. Rinse 
absorber and its connecting tubing sparingly with distilled water 
and add to flask. Dilute to volume with distilled water and mix 
thoroughly. 

e. Determine cyanide concentration in the absorption solution 
by procedure of 4500-CN". D, E, or F. 

/*. Distillation gives quantitative recovery of even refractory 
cyanides such as iron complexes. To obtain complete recovery 
of cobalticyanide use ultraviolet radiation pretreatment. 1 - 2 If in- 
complete recovery is suspected, distill again by refilling the gas 
washer with a fresh charge of NaOH solution and refluxing 1 h 
more. The cyanide from the second reflux, if any, will indicate 
completeness of recovery. 

g. As a quality control measure, periodically test apparatus, 
reagents, and other potential variables in the concentration range 
of interest. As an example at least 100 ± 4% recovery from 1 
mg CN~/L standard should be obtained. 

5. References 

1. Casapieri, P., R. Scott & E.A. Simpson. 1970. The determination 
of cyanide ions in waters and effluents by an Auto Analyzer proce- 
dure. Anal. Own. Acta 49:188. 

2. Goulden, P.D., K.A. Badar & P. Brooksbank. 1972. Determi- 
nation of nanogram quantities of simple and complex cyanides in 
water. Anal. Chem. 44:1845. 



4-24 



INORGANIC NONMETALS (4000) 



4500-CN- D. Titrimetric Method 



1 . General Discussion 

a. Principle: CN " in the alkaline distillate from the preliminary 
treatment procedure is titrated with standard silver nitrate ( AgN0 3 ) 
to form the soluble cyanide complex, Ag(CN) 2 ~. As soon as all 
CN~ has been complexed and a small excess of Ag" has been 
added, the excess Ag f " is detected by the silver-sensitive indi- 
cator, /7-dirnethylarninobenzalrhodanine, which immediately turns 
from a yellow to a salmon color. 1 The distillation has provided 
a 2:1 concentration. The indicator is sensitive to about 0.1 mg 
Ag/L. If titration shows that CN" is below 1 mg/L, examine 
another portion colorimetrically or potentiometrically. 

2. Apparatus 

Koch micro buret, 10-mL capacity. 

3. Reagents 

a. Indicator solution: Dissolve 20 mgp-dimethylaminobenzal- 
rhodanine in 100 mL acetone. 

b. Standard silver nitrate titrant: Dissolve 3.27 g AgNO-, in 1 
L distilled water. Standardize against standard NaCl solution, 
using the argentometric method with KXrO., indicator, as di- 
rected in Chloride, Section 4500-C1-.B. 

Dilute 500 mL AgN0 3 solution according to the titer found 
so that LOO mL is equivalent to 1.00 mg CN*. 

c. Sodium hydroxide dilution solution: Dissolve 1.6 g NaOH 
in 1 L distilled water. 

4. Procedure 

a. From the absorption solution take a measured volume of 
sample so that the titration will require approximately 1 to 10 
mL AgN0 3 titrant. Dilute to 100 mL using the NaOH dilution 
solution or to some other convenient volume to be used for all 
titrations. For samples with low cyanide concentration (<5 mg/ 
L) do not dilute. Add 0.5 mL indicator solution. 

b. Titrate with standard AgN0 3 titrant to the first change in 
color from a canary yellow to a salmon hue. Titrate a blank 
containing the same amount of alkali and water, i.e., 100 mL 
NaOH dilution solution (or volume used for sample). As the 
analyst becomes accustomed to the end point, blank titrations 
decrease from the high values usually experienced in the first 
few trials to 1 drop or less, with a corresponding improvement 
in precision. 



5. Calculation 



(A - B) x 1000 
mg CN'/L - — rr 2 -. r x 



250 



mL original sample mL portion used 



where: 

A = mL standard AgN0 3 for sample and 
B = mL standard AgN0 3 for blank. 



6. Precision and Bias 2 

Based on the results of six operators in three laboratories, the 
overall and single-operator precision of this method within its 
designated range may be expressed as follows: 

Reagent water: S r = 0.04* + 0.038 
S, - O.Olx + 0.018 

Selected water matrices: S y = 0.06x -f- 0.71 1 
S„ - 0.04* + 0.027 



where: 

S„ : 



overall precision, mg/L, 
single-operator precision, mg/L, and 
cyanide concentration, mg/L. 



Recoveries of known amounts of cyanide from Type II reagent 
water and selected water matrices are: 





Added 


Recovered 










Medium 


mg/L 


mg/L 


n 


S T 


Bias 


% Bias 


Reagent 


2.00 


2.10 


18 


0.1267 


0.10 


5 


water 


5.00 


4.65 


18 


0.2199 


-0.35 


-7 




5.00 


5.18 


18 


0.2612 


0.18 


4 


Selected 


2.00 


2.80 


18 


0.8695 


0.80 


40 


water 


5.00 


5.29 


18 


1.1160 


0.29 


6 


matrices 


5.00 


5.75 


18 


0.9970 


0.75 


15 



7. References 

1. Ryan, J. A. & G.W. Culshaw. 1944. The use of /?-dimethylamino- 
benzylidene rhodanine as an indicator for the volumetric determi- 
nation of cyanides. Analyst 69:370. 

2. American Society for Testing & Materials. 1987. Research Rep. 
D2036-.19-1 131. American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" E. Colorimetric Method 



1. General Discussion 

a. Principle: CN in the alkaline distillate from preliminary 
treatment is converted to CNCl by reaction with chloramine-T 
at pH <8 without hydrolyzing to CNO ,' (Caution — CNCl is 



a toxic gas; avoid inhalation.) After the reaction is complete, 
CNCl forms a red-blue color on addition of a pyridine-barbituric 
acid reagent. Maximum color absorbance in aqueous solution is 
between 575 and 582 nm. To obtain colors of comparable inten- 
sity, have the same salt content in sample and standards. 



CYANIDE (4500-CN-)/Colorimetric Method 



4-25 



b. Interference: All known interferences are eliminated or re- 
duced to a minimum by distillation. 

2. Apparatus 

Colorimetric equipment: One of the following is required: 

a. Spectrophotometer, for use at 578 nm, providing a light path 
of 10 mm or longer. 

b. Filter photometer, providing a light path of at least 10 mm 
and equipped with a red filter having maximum transmittance 
at 570 to 580 nm. 

3. Reagents 

a. Chloramine-T solution: Dissolve 1.0 g white, water-soluble 
powder in 100 mL water. Prepare weekly and store in refriger- 
ator. 

b. Stock cyanide solution: Dissolve approximately 1 .6 g NaOH 
and 2.51 g KCN in 1 L distilled water. (Caui ion— KCN is highly 
toxic; avoid contact or inhalation.) Standardize against standard 
silver nitrate (AgN0 3 ) titrant as described in Section 4500-CN D.4, 
using 25 mL KCN solution. Check titer weekly because the so- 
lution gradually loses strength; 1 mL = 1 mg CN". 

c. Standard cyanide solution: Based on the concentration de- 
termined for the KCN stock solution (11 3b) calculate volume 
required (approximately 10 mL) to prepare 1 L of a 10 |xg CN~/ 
mL solution. Dilute with the NaOH dilution solution. Dilute 10 
mL of the 10 jxg CN "/mL solution to 100 mL with the NaOH 
dilution solution; 1.0 mL - 1.0 |xg CN". Prepare fresh daily 
and keep in a glass-stoppered bottle. (Caution — Toxic; take 
care to avoid ingestion.) 

d. Pyridine-barbituric acid reagent: Place 15 g barbituric acid 
in a 250-mL volumetric flask and add just enough water to wash 
sides of flask and wet barbituric acid. Add 75 mL pyridine and 
mix. Add 15 mL cone hydrochloric acid (HCI), mix, and cool to 
room temperature. Dilute to volume and mix until barbituric 
acid is dissolved. The solution is stable for approximately 6 months 
if stored in an amber bottle under refrigeration; discard if pre- 
cipitate develops. 

e. Acetate buffer: Dissolve 410 g sodium acetate trihydrate, 
NaC 2 H 1 2 '3H 2 0, in 500 mL of water. Add glacial acetic acid to 
adjust to pH 4.5, approximately 500 mL. 

/. Sodium hydroxide dilution solution; Dissolve 1.6 g NaOH 
in 1 L distilled water. 

4. Procedure 

a. Preparation of standard curve: Pi pet a series of standards 
containing I to 10 |xg CN into 50-mL volumetric flasks (0.02 
to 0.2 jag CN /mL). Dilute to 40 mL with NaOH dilution so- 
lution. Use 40 mL of NaOH dilution solution as blank. Develop 
and measure absorbance in 10-mm cells as described in S\ b for 
both standards and blank. For concentrations lower than 0.02 
jmg CN VmL use 100-mm cells. 

Recheck calibration curve periodically and each time a new 
reagent is prepared. 

/>. Color development: Pipet a portion of absorption solution 
into a 50-mL volumetric flask and dilute to 40 mL with NaOH 
dilution solution. Add 1 mL acetate buffer and 2 mL chloramine- 
T solution, stopper, and mix by inversion twice. Let stand exactly 
2 min. 



Add 5 mL pyridine-barbituric acid reagent, dilute to volume 
with distilled water, mix thoroughly, and let stand exactly 8 min. 
Measure absorbance against distilled water at 578 nm. 

Measure absorbance of blank (0.0 mg CN~/L) using 40 mL 
NaOH dilution solution and procedures for color development. 

5. Calculation 

Use the linear regression feature available on most scientific 

calculators, or compute slope and intercept of standard curve as 

follows: 

n 2 ca ~~ 2 c 2 a 

m - — — 

n 2 a- - {2 a)~ 

2 a 2 2 c - 2 a 2 ac 



y - 



(2 ay- 



where: 

a = absorbance oi standard solution. 
c — concentration of CN~ in standard, mg/L, 
n — number of standard solutions, 
m = slope of standard curve, and 
b = intercept on c axis. 

Include the blank concentration, 0.0 mg CN"/L and blank 
absorbance in the calculations above. 

CN"', mg/L = (ma x + b) x "— x — - 
X Y 

where: 

X = absorption solution, mL, 
Y — original sample, mL, and 
a i — absorbance of sample solution. 

6. Precision and Bias 2 

Based on the results of nine operators in nine laboratories, 
the overall and single-operator precision of this method within 
its designated ranges may be expressed as follows: 

Reagent water: S r = 0.06* + 0.003 
S„ - O.IU + 0.010 



Selected water matrices: S T 



0.04* + 0:018 
0.04* + 0.008 



where: 

Sj — overall precision, mg/L, 

S = single-operator precision, mg/L, and 

x = cyanide concentration, mg/L. 

Recoveries of known amounts of cyanide from Type II reagent 
water and selected water matrices (coke plant and refinery wastes, 
sewage, and surface water) are: 





Added 


Recovered 










Medium 


mg/L 


mg/L 


n 


S T 


Bias 


% Bias 


Reagent 


0.060 


0.060 


26 


0.0101 


0.000 





water 


0.500 


0.480 


23 


0.0258 


-0.020 


-4 




0.900 


0.996 


27 


0.0669 


0.096 


11 


Selected 


0.060 


0.060 


25 


0.0145 


0.000 





water 


0.500 


0.489 


26 


0.0501 


-0.011 


-3 


matrices 


0.900 


0.959 


24 


0.0509 


0.059 


7 



4-26 



INORGANIC NONMETALS (4000) 



7. References 

1. Amus, E. & H. Garschagen. 1953, Uber die Verwendung der Bar- 
bitsaure fur die photometrische Bestimmund von Cyanid und Rho- 
danid. Z. Anal. Chem. 138:414. 



2. American Society for Testing & Materials. 1987. Research Rep. 
D2036:19-1133 . American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN ~ F. Cyanide-Selective Electrode Method 



1. General Discussion 

CN" in the alkaline distillate from the preliminary treatment 
procedures can be determined potentiometrically by using a CN~- 
selective electrode in combination with a double-junction ref- 
erence electrode and a pH meter having an expanded millivolt 
scale, or a specific ion meter. This method can be used to de- 
termine CN" concentration in place of either the colorimetric 
or titrimetric procedures in the concentration range of 0.05 to 
10mgCN"/L. I_3 If the CN "-selective electrode method is used, 
the previously described titration screening step can be omitted. 

2. Apparatus 

a. Expanded-scale pH meter or specific-ion meter. 

b. Cyanide-ion-selective electrode.* 

c. Reference electrode, double- junction. 

d. Magnetic mixer with TFE-coated stirring bar. 

e. Koch microburet, 10-mL capacity. 

3. Reagents 

a. Stock standard cyanide solution: See Section 4500-CN .E. 3b. 

b. Sodium hydroxide dilution solution: Dissolve 1.6 g NaOH 
in water and dilute to 1 L. 

c. Standard cyanide solution: Dilute a calculated volume (ap- 
proximately 25 ml) of stock KCN solution, based on the deter- 
mined concentration, to 1000 mL with NaOH diluent. Mix thor- 
oughly; 1 mL 25 \xg CN" . 

d. Dilute standard cyanide solution: Dilute 100.0 mL standard 
CN' solution to 1000 mL with NaOH diluent; 1.00 mL - 2.5 
jxg CN" . Prepare daily and keep in a dark, glass-stoppered bot- 
tle. 

e. Potassium nitrate solution: Dissolve 100 g KN0 3 in water 
and dilute to 1 L. Adjust to pH 12 with KOH. This is the outer 
filling solution for the double-junction reference electrode. 



2.5, 0.25, 0.125, and 0.025 \xg CN"7mL in NaOH dilution so- 
lution. Transfer approximately 100 mL of each of these standard 
solutions into a 250-mL beaker prerinsed with a small portion 
of standard being tested. Immerse CN* and double-junction 
reference electrodes. Mix well on a magnetic stirrer at 25°C, 
maintaining as closely as possible the same stirring rate for all 
solutions. 

Always progress from the lowest to the highest concentration 
of standard because otherwise equilibrium is reached only slowly. 
The electrode membrane dissolves in solutions of high CN" con- 
centration; do not use with a concentration above 25 \xg CN~/ 
mL. After making measurements remove electrode and soak in 
water. 

After equilibrium is reached (at least 5 min and not more than 
10 min), record potential (millivolt) readings. Plot CN~ concen- 
tration on logarithmic axis of semilogarithmic paper versus po- 
tential developed in solution on linear axis. A straight line with 
a slope of approximately 59 mV per decade indicates that the 
instrument and electrodes are operating properly. Record slope 
of line obtained (millivolts/decade of concentration). The slope 
may vary somewhat from the theoretical value of 59.2 mV per 
decade because of manufacturing variation and reference elec- 
trode (liquid-junction) potentials. The slope should be a straight 
line and is the basis for calculating sample concentration. Follow 
manufacturer's instructions for direct-reading ion meters. 

b. Measurement of sample: Place 100 mL of absorption liquid 
obtained in Section 4500-CN ".C.4d (or an accurately measured 
portion diluted to 100 mL with NaOH dilution solution) into a 
250-mL beaker. When measuring low CN" concentrations, first 
rinse beaker and electrodes with a small volume of sample. Im- 
merse CN~ and double-junction reference electrodes and mix 
on a magnetic stirrer at the same stirring rate used for calibration. 
After equilibrium is reached (at least 5 min and not more than 
10 min), record values indicated on ion meter or found from 
graph prepared as above. Calculate concentration as directed 
below. 



4. Procedure 

a. Calibration: Using Koch microburet and standard CN" so- 
lution, prepare four (or more) additional solutions containing 



* Orion Model 94-06 A or equivalent. 



5. Calculations 

100 250 
mg CN~/L = (xg CN"/mL from graph or meter x X 

where: 

x = volume of absorption solution, mL, and 
v - volume of original sample, mL. 



CYANIDE (4500-CN~)/Amenable to Chlorination after Distillation 



4-27 



6. Precision and Bias 4 

The precision of the CN~ -ion-selective electrode method using 
the absorption solution from total cyanide distillation has been 
found in collaborative testing to be linear within its designated 
range. 

Based on the results of six operators in five laboratories, the 
overall and single-operator precision of this method within its 
designated range may be expressed as follows: 

Reagent water: S T = 0.06* + 0.003 
S„ - 0.03jc + 0.008 



Selected water matrices: S r 
S„ 



0.05* + 0.008 
0.03x + 0.012 



where 
S„ 



overall precision, mg/L, 
single-operator precision, mg/L, and 
x - cyanide concentration, mg/L. 



Recoveries of known amounts of cyanide from Type II reagent 
water and selected water matrices are: 





Added 


Recovered 










Medium 


mg/L 


mg!L 


n 


S T 


Bias 


% Bias 


Reagent 


0.060 


0.059 


18 


0.0086 


-0.001 


2 


water 


0.500 


0.459 


18 


0.0281 


-0.041 


-8 




0.900 


0.911 


18 


0.0552 


0.011 


1 




5.00 


5.07 


18 


0.297 


0.07 


1 


Selected 


0.060 


0.058 


14 


0.0071 


-0.002 


-3 


water 


0.500 


0.468 


21 


0.04 J 4 


-0.032 


-6 


matrices 


0.900 


0.922 


19 


0.0532 


0.022 


2 




5.00 


5.13 


20 


0.2839 


0.13 


3 



7. References 

1. Orion Research, Inc. 1975. Cyanide Ion Electrode Instruction Man- 
ual. Cambridge, Mass. 

2. Frant, M.S., J.W. Ross& J.H. Riseman. 1972. An electrode in- 
dicator technique Tor measuring low levels of cyanide. Anal. Chem. 
44:2227. 

3. Sekerka, J. & J.F. Lechner. 1976. Potentiometric determination of 
low levels of simple and total cyanides. Water Res. 10:479." 

4. American Society for Testing & Materials. 1987. Research Rep. 
D2036: 19-1 131. American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" G. Cyanides Amenable to Chlorination after Distillation 



1. General Discussion 

This method is applicable to the determination of cyanides 
amenable to chlorination. 

After part of the sample is chlorinated to decompose the cy- 
anides, both the chlorinated and the untreated sample are sub- 
jected to distillation as described in Section 4500-CN ~.C. The 
difference between the CN " concentrations found in the two 
samples is expressed as cyanides amenable to chlorination. 

Some unidentified organic chemicals may oxidize or form 
breakdown products during chlorination, giving higher results 
for cyanide after chlorination than before chlorination. This may 
lead to a negative value for cyanides amenable to chlorination 
after distillation for wastes from, for example, the steel industry, 
petroleum refining, and pulp and paper processing. Where such 
interferences are encountered use Method 4500-CN". I for de- 
termining dissociable cyanide. 

Protect sample from exposure to ultraviolet radiation, and 
perform manipulations under incandescent light, to prevent pho- 
todecomposition of some metal-cyanide complexes by ultraviolet 
light. 

2. Apparatus 

a. Distillation apparatus: See Section 4500-CN ~\C. 2 

b. Apparatus for determining cyanide by either the titrimetric 
method, Section 4500-CN .D. 2, the colorimetric method, Sec- 
tion 4500-CN ".E. 2, or the electrode method, Section 4500- 
CN. F.2. 



3. Reagents 

a. All reagents listed in Section 4500-CN ~ .C. 3. 

b. All reagents listed in Section 4500-CN~ .D.3, 4500-CN~.E3, 
or 4500-CN' .F. 3, depending on method of estimation. 

c. Calcium hypochlorite solution: Dissolve 5 g Ca(OCl) 2 in 100 
mL distilled water. Store in an amber-colored glass bottle in the 
dark. Prepare monthly. 

d. Potassium iodide(KI)-starch test paper. 

4. Procedure 

a. Divide sample into two equal portions of 500 mL (or equal 
portions diluted to 500 mL) and chlorinate one as in H b below. 
Analyze both portions for CN". The difference in determined 
concentrations is the cyanide amenable to chlorination. 

b. Place one portion in a 1-L beaker covered with aluminum 
foil or black paper. Keep beaker covered with a wrapped watch 
glass during chlorination. Add Ca(OCl) 2 solution dropwise to 
sample while agitating and maintaining pH between 11 and 12 
by adding NaOH solution. Test for chlorine by placing a drop 
of treated sample on a strip of Kl-starch paper. A distinct blue 
color indicates sufficient chlorine (approximately 50 to 100 mg 
Cl 2 /L). Maintain excess residual chlorine for 1 h while agitating. 
If necessary, add more Ca(OCl) 2 and/or NaOH. 

c. After 1 h remove any residual chlorine by dropwise addition 
of NaAsO, solution (2 g/100 mL) or by addition of 8 drops H 2 2 
(3%) followed by 4 drops Na 2 S 2 0, solution (500 g/L). Test with 
Kl-starch paper until there is no color change. 



4-28 



INORGANIC NONMETALS (4000) 



d. Distill both chlorinated and unchlorinated samples as in 
Section 4500-CN \C. Test according to Methods D, E, or F. 



5. Calculation 



mti CN " amenable to chlorination/L 



H 



where: 
G 
H 



mg CN~/L found in unchlorinated portion of sample and 
mg CN""/L found in chlorinated portion of sample. 



For samples containing significant quantities of iron cyanides, 
it is possible that the second distillation will give a higher value 
for CN" than the test for total cyanide, leading to a negative 
result. When the difference is within the precision limits of the 
method, report, 4t no determinable quantities of cyanide ame- 
nable to chlorination." If the difference is greater than the pre- 
cision limit, ascertain the cause such as presence of interferences, 
manipulation of the procedure, etc., or use Method I. 



6. Precision and Bias 1 

The precision and bias information given in this section may 
not apply to waters of untested matrices, 
a. Precision: 

1) Colorimetric — Based on the results of eight operators in 
seven laboratories, the overall and single-operator precision of 
this test method within its designated range may be expressed 
as follows: 

Reagent water: S r = O.l&e + 0.005 
S n = 0.06* + 0.003 

Selected water matrices: S r = 0.20* -f 0.009 
S - 0.05* +■ 0.005 

2) Titrimetric — Based on the results of six operators in three 



laboratories, the overall and single-operator precision of this test 
method within its designated range may be expressed as follows: 

Reagent water: S r - 0.01* + 0.439 
5 = 0.241 - 0.03* 



Selected water matrices: S r 



0.12* + 0.378 
0.209 - 0.01* 



where: 

S i — overall precision, mg/L, 

S a — single-operator precision, mg/L, and 

* = cyanide concentration, mg CN /L 

b. Bias: Recoveries of known amount of cyanide amenable to 
chlorination from Type II reagent water and selected water mat- 
rices are shown below: 







Added 


Recovered 








% 


Medium 


Technique 


mg/L 


mg/L 


n 


Sr 


Bias 


Bias 


Reagent 


Colorimetric 


0.008 


0.009 


21 


0.0033 


0.001 


13 


water 




0.019 


0.023 


20 


0.0070 


0.004 


21 






0.080 


0.103 


20 


0.0304 


0.018 


23 






0.191 


0.228 


21 


0.0428 


0.037 


19 




Titrimetric 


1.00 


0.73 


18 


0.350 


-0.27 


-27 






1.00 


0.81 


18 


0.551 


-0.19 


-19 






4.00 


3.29 


18 


0.477 


-0.7 J 


-18 


Selected 


Colorimetric 


0.008 


0.013 


17 


0.0077 


0.005 


63 


water 




0.019 


0.025 


18 


0.0121 


0.006 


32 


matrices 




0.080 


0.100 


18 


0.0372 


0.020 


25 






0.191 


0.229 


18 


0.0503 


0.038 


20 




Titrimetric 


1.00 


1.20 


18 


0.703 


0.20 


20 






1.00 


1 . 10 


18 


0.328 


0.10 


10 






4.00 


3.83 


18 


0.818 


-0.17 


-4 



7. Reference 

1. American Society for Testing & Materials. 1987. Research Rep. 
D2036: 19-1 131 . American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" H. Cyanides Amenable to Chlorination without Distillation (Short-Cut Method) 



1. General Discussion 

This method covers the determination of HCN and of CN 
complexes that are amenable to chlorination and also thiocya- 
nates (SCN~). The procedure does not measure cyanates (CNO") 
or iron cyanide complexes, but does determine cyanogen chloride 
(CNCl). It may be modified for use in presence of thiocyanates. 
The method requires neither lengthy distillation nor the chlori- 
nation of one sample before distillation. The recovery of CN" 
from metal cyanide complexes will be comparable to that in 
Methods G and I. 

The cyanides are converted to CNCl by chloramine-T after 
the sample has been heated. In the absence of nickel, copper, 
silver, and gold cyanide complexes or SCN", the CNCl may be 
developed at room temperature. The pyridine-barbituric acid 
reagent produces a red-blue color in the sample. The color can 
be estimated visually against standards or photometrically at 578 



nm. The dissolved salt content in the standards used for the 
development of the calibration curve should be near the salt 
content of the sample, including the added NaOH and phosphate 
buffer. 

The method's usefulness is limited by thiocyanate interference. 
Although the procedure allows the specific determination of CN~ 
amenable to chlorination (see 4500-CN" .H.2 and 5) by masking 
the CN " content and thereby establishing a correction for the 
thiocyanide content, the ratio of SCN " to CN ~ should not exceed 
3 to be applicable. Tn working with unknown samples, screen 
the sample for SCN" by the spot test (4500-CN". K). 



2. Interferences 

a. Remove interfering agents as described in Section 4500- 
CN - .B with the exception of NO," and N0 3 " (4500-CN" .B.3/i). 



CYANIDE (4500-CN )/Amenable to Chlorination without Distillation 



4-29 



b. The SCN " ion reacts with chloramine-T to give a positive 
error equivalent to its concentration, The procedure allows the 
separate determination of SCN" and subtraction of this value 
from the results for the total. Use the spot test (4500-CN ~.K) 
for SCN" when its presence is suspected, If the SCN content 
is more than three times the CN content, use Method G or I. 

c. Reducing chemical compounds, such as S0 3 2 " , may inter- 
fere by consuming chlorine in the chloramine-T addition. A sig- 
nificant excess of chlorine is provided, but the procedure pre- 
scribes a test (4500-CN ~ \H.5d) to avoid this interference. 

d. Color and turbidity may interfere with the colorimetric de- 
termination. Overcome this interference by extraction with chlo- 
roform (4500-CN". B. 3c) but omit reduction of the pH. Other- 
wise, use Method G or I. 

Compensation for color and turbidity may be made by deter- 
mining absorbance of a second sample solution to which all re- 
agents except chloramine-T have been added. 

e. Color intensity and absorption are affected by wide varia- 
tions in total dissolved solids content of the sample. 

For samples containing high concentrations of dissolved solids 
(3000 to 10 000 mg/L), add 6 g NaCl/L NaOH solution (1.6 g/ 
L) used to prepare standards. For samples containing dissolved 
solids concentrations greater than 10 000 mg/L, add sufficient 
NaCl to the NaOH solution to approximate the dissolved solids 
content. 



3. Apparatus 

a . App a ra t us listed in 4500-CN ~\E. 2. 

b. Hot water bath. 



4. Reagents 

a. Reagents listed in Sections 4500-CN ' .B and E.3. 

b. Sodium chloride, NaCl, crystals. 

c. Sodium carbonate, Na 2 C0 3 , crystals. 

d. Sulfuric acid solution, H 2 S0 4 , 1/V. 

e. EDTA solution, 0.05 A// Dissolve 18.5 g disodium salt of 
ethylenediamine tetraacetic acid in water and dilute to 1 L. 

/. Formaldehyde solution, 10%: Difute 27 mL formaldehyde 
(37% pharmaceutical grade) to 100 mL. 

g. Phosphate buffer: Dissolve 138 g sodium dihydrogen phos- 
phate monohydrate, NaH 2 PO i ,-H 2 0, in water and dilute to 1 L. 
Refrigerate. 



b. Adjust pH of 50 mL sample to between 11.4 and 11.8. If 
acid is needed, add a small amount (0.2 to 0.4 g) of sodium 
carbonate and stir to dissolve. Then add HC1 solution (1 + 9) 
dropwise while stirring. For raising the pH, use NaOH solution 
(40 g/L). 

c. Pipet 20.0 mL of adjusted sample into a 50-mL volumetric 
flask. If the cyanide concentration is greater than 0.3 mg/L, use 
a smaller portion and dilute to 20 mL with NaOH solution. Do 
not exceed the concentration limit of 0.3 mg/L. 

d. To insure uniform color development, both in calibration 
and testing, maintain a uniform temperature. Immerse flasks in 
a water bath held at 27 ± 1°C for 10 min before adding reagents 
and keep samples in water bath until all reagents have been 
added. 

Add 4 mL phosphate buffer and swirl to mix. Add one drop 
of EDTA solution, and mix. 

e. Add 2 mL chloramine-T solution and swirl to mix. Place 1 
drop of sample on potassium iodide-starch test paper that has 
been moistened previously with acetate buffer solution. Repeat 
the chloramine-T addition if required. After exactly 3 min, add 
5 mL pyridine-barbituric acid reagent and swirl to mix. 

/'. Remove samples from water bath, dilute to volume, and 
mix. Allow 8 min from the addition of the pyridine-barbituric 
acid reagent for color development. 

Determine absorbance at 578 nm in a 1.0-cm cell versus dis- 
tilled water. 

Calculate concentration of cyanide, mg/L in the original sam- 
ple following instructions given in 4500-CN" E. 

g. If the presence of thiocyanate is suspected, pipet a second 
20-mL portion of pH-adjusted sample into a 50-mL volumetric 
flask. Add 3 drops 10% formaldehyde solution. Mix and let stand 
10 min. Place in a water bath at 27 ± ]°C for an additional 10 
min before the addition of the reagent chemicals and hold in the 
bath until all reagents have been added. 

Continue with b above. 

Calculate the concentration of cyanide, as milligrams per liter, 
in the original sample following instructions given in 4500-CN" . 
E. 

h. In the presence of thiocyanate, cyanide amenable to chlo- 
rination is equal to the difference between the concentrations of 
cyanide obtained in f and g. 



6. Calculation 

See 4500-CN ~.E. 5. 

Deduct SCN value from the results found when the CN ~ has 
not been masked by formaldehyde addition (total) for cyanide 
content. 



5. Procedure 

a. Calibrate as directed in Section 4500-CN .E. \a and 4a. For 
samples with more than 3000 mg total dissolved solids/L, prepare 
a calibration curve from standards and blank NaOH solutions 
containing 6 g NaCl/L. Samples containing total dissolved solids 
exceeding 10 000 mg/L require appropriate standards and a new 
calibration curve. 



7. Precision and Bias 1 

This precision and bias information may not apply to waters 
of untested matrices. 

a. Precision: Based on the results of 14 operators in nine lab- 
oratories, the overall and single-operator precision of this test 
method within its designated range may be expressed as follows: 



4-30 



INORGANIC NONMETALS (4000) 



Reagent water: S T 



O.lOx + 0.006 
0.07* + 0.005 



Selected water matrices: S T = 0.1 lx -f- 0.007 
S a - 0.02* + 0.005 



where: 

S T = overall precision, mg/L, 

S ~ single-operator precision. mg/L, and 

x — cyanide concentration, mg/L. 



b. Bias: Recoveries of known amounts of cyanide from Type 
II reagent water and selected water matrices including creek 
waters, diluted sewage (1 to 20), and industrial wastewater are 
shown below. 





Added mg/L 


Recovered 








% 


Medium 


CN" 


SCN~ 


mgiL 


n 


S T 


Bias 


Bias 


Reagent 


0.005 




0.007 


42 


0.0049 


0.002 


40 


water 


0.027 




0.036 


41 


0.0109 


0.009 


25 




0.090 




0.100 


42 


0.0167 


0.010 


11 




0.090 


0.080 


0.080 


39 


0.0121 


-0.010 


11 




0.270 




0.276 


42 


0.0320 


0.006 


2 


Selected 


0.005 




0.003 


40 


0.0042 


-0.002 


40 


water 


0.027 




0.026 


42 


0.0093 


-0.001 


4 


matrices 


0.090 




0.087 


42 


0.0202 


-0.003 


3 




0.090 


0.080 


0.068 


37 


0.0146 


-0.022 


24 




0.270 




0.245 


41 


0.0319 


-0.025 


9 



8. Reference 

1. American Society for Testing & Materials. 1987. Research Rep. 
D2036: 19-1074. American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" I. Weak Acid Dissociable Cyanide 



1 . General Discussion 

Hydrogen cyanide (HCN) is liberated from a slightly acidified 
(pH 4.5 to 6.0) sample under the prescribed distillation condi- 
tions. The method does not recover CN~ from tight complexes 
that would not be amenable to oxidation by chlorine. The acetate 
buffer used contains zinc salts to precipitate iron cyanide as a 
further assurance of the selectivity of the method. In other re- 
spects the method is similar to 4500-CN".C. 

2. Interferences 

See45G0-CN-.B.3. 

Protect sample and apparatus from ultraviolet light to prevent 
photodecomposition of some metal-cyanide complexes and an 
increase in concentration of weak acid dissociable cyanide. 

If procedure is used to determine low concentrations of cyanide 
in samples of ferri- and ferrocyanide, add more, e.g., fivefold 
excess, zinc acetate solution before adding acid and distilling. 

3. Apparatus 

See Section 4500-CN~,C2 and Figure 4500-CN~:l, and also 
Section 4500-CN-.D.2, 4500-CN~.E.2, or 4500-CN~.F.2, de- 
pending on method of estimation. 

4. Reagents 

a. Reagents listed in Section 4500-CN~ .C.3. 

b. Reagents listed in Section 4500-CN-.D.3, 4500-CN~.E.3, 
or 4500~CN~.F.3, depending on method of estimation. 

c. Acetic acid, 1 + 9: Mix 1 volume of glacial acetic acid with 
9 volumes of water. 

d. Acetate buffer: Dissolve 410 g sodium acetate trihydrate 
(NaC 2 H 3 2 -3H 2 0) in 500 mL water. Add glacial acetic acid to 
yield a solution pH of 4.5 (approximately 500 mL). 



e. Zinc acetate solution, 100 g/L: Dissolve 120 g 
Zn(C 2 H 3 2 ) 2 -H 2 in 500 mL water. Dilute to 1 L. 
/. Methyl red indicator. 



5. Procedure 

Follow procedure described in 4500-CN~.C4, but with the 
following modifications: 

a. Do not add sulfamic acid, because N0 2 ~" and N0 3 ~ do not 
interfere. 

b. Instead of H 2 S0 4 and MgCl 2 reagents, add 20 mL each of 
the acetate buffer and zinc acetate solutions through air inlet 
tube. Also add 2 to 3 drops methyl red indicator. Rinse air inlet 
tube with water and let air mix contents. If the solution is not 
pink, add acetic acid (1 + 9) dropwise through air inlet tube 
until a pink color persists. 

c. Follow instructions beginning with 4500-CN~.C.4d. 

d. For determining CN~ in the absorption solution, use the 
preferred finish method (4500-CN~.D, E, or F). 



6. Precision and Bias 1 

The precision and bias information given in this section may 
not apply to waters of untested matrices. 

a. Precision: 

1) Colorimetric — Based on the results of nine operators in 
nine laboratories, the overall and single-operator precision of 
this test method within its designated range may be expressed 
as follows: 

Reagent water: S r = 0.09* + 0.010 
S - 0.08x 4- 0.005 

Selected water matrices: S T = 0.08x + 0.012 
S - 0.05* + 0.008 



CYANIDE (4500-CN -)/Cyanogen Chloride 



4-31 



2) Electrode — Based on the results of six operators in five 
laboratories, the overall and single-operator precision of this test 
method within its designated range may be expressed as follows: 



Reagent water: S T = 0.09* + 0.004 
S a = 0.02* ~ 0.009 



Selected water matrices: S r 



0.08* + 0.005 
0.02* + 0.004 



3) Titrimetric — Based on the results of six operators in three 
laboratories, the overall and single-operator precision of this test 
method within its designated range may be expressed as follows: 

Reagent water: S T - 0.532 - 0.10* 
S a = 0.151 - 0.01* 

Selected water matrices: S T = 0,604 - 0.06* 
S a - 0.092 + 0.02* 

where: 

5 7 . = overall precision, 
S — single-operator precision, and 
* = cyanide concentration, mg/L. 



b. Bias: Recoveries of known amounts of cyanide from Type 
II reagent water and selected water matrices are shown below. 







Added 


Recovered 








% 


Medium 


Technique 


mg/L 


mg/L 


n 


Sr 


Bias 


Bias 


Reagent 


Colorimetric 


0.030 


0.030 


25 


0.0089 


0.000 





water 




0.100 


0.1 17 


27 


0.0251 


0.017 


17 






0.400 


0.361 


27 


0.0400 


-0.039 


-10 




Electrode 


0.030 


0.030 


21 


0.0059 


0.000 









0.100 


0.095 


21 


0.0163 


-0.005 


»5 






0.400 


0.365 


21 


0.0316 


-0.035 


-9 






1.000 


0.940 


21 


0.0903 


-0.060 


-6 




Titrimetric 


1.00 


1.35 


18 


0.4348 


0.35 


35 






1.00 


1.38 


18 


0.3688 


0.38 


38 






4.00 


3.67 


18 


0.1830 


-0.33 


-8 


Selected 


Colorimetric 


0.030 


0.029 


15 


0.0062 


0.001 


3 


water 




0.100 


0.118 


24 


0.0312 


0.018 


18 


matrices 




0.400 


0.381 


23 


0.0389 


-0.019 


-5 




Electrode 


0.030 


0.029 


20 


0.0048 


-0.001 


-3 






0.100 


0.104 


2i 


0.0125 


0.004 


4 






0.400 


0.357 


21 


0.0372 


-0.043 


-11 






1.000 


0.935 


21 


0.0739 


- 0.065 


-7 




Titrimetric 


1.00 


1.55 


18 


0.5466 


0.55 


55 






1.00 


1.53 


18 


0.4625 


0.53 


53 






4.00 


3.90 


18 


0.3513 


-0.10 


-3 



7. Reference 

I . American Society for Testing & Materials. 1987. Research Rep. 
D2036T9-1 131. American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" J. Cyanogen Chloride 



1 . Genera! Discussion 

Cyanogen chloride (CNC1) is the first reaction product when 
cyanide compounds are chlorinated. It is a volatile gas, only 
slightly soluble in water, but highly toxic even in low concentra- 
tions. (Caution: Avoid inhalation or contact.) A mixed pyridine- 
barbituric acid reagent produces a red-blue color with CNCl. 

Because CNCl hydrolyzes to cyanate (CNO~) at a pH of 12 
or more, collect a separate sample for CNCl analysis (See Section 
4500-CN ~.B. 2) in a closed container without sodium hydroxide 
(NaOH). A quick test with a spot plate or comparator as soon 
as the sample is collected may be the only procedure for avoiding 
hydrolysis of CNCl due to time lapse between sampling and 
analysis. 

If starch-iodide (KI) test paper indicates presence of chlorine 
or other oxidizing agents, add sodium thiosulfate (Na 2 S 2 3 ) im- 
mediately as directed in Section 4500-CN ~.B. 2. 

2. Apparatus 

See Section 4500-CN ~".E. 2. 



3. Reagents 

a. Reagents listed in Sections 4500-CN". E. 3 and 4500-CN" . H.4. 



b. Phosphate buffer: Dissolve 138 g sodium dihydrogen phos- 
phate monohydrate, NaH 2 P0 4 H 2 0, in water and dilute to 1 L. 
Refrigerate. 

4. Procedure 

a. Preparation of standard curve: Pipet a series of standards 
containing 1 to 10 jxg CN~ into 50-mL volumetric flasks (0.02 
to 0.2 fig CN"/mL). Dilute to 20 mL with NaOH dilution so- 
lution. Use 20 mL of NaOH dilution solution for the blank. Add 

2 mL chloramine-T solution and 4 mL phosphate buffer; stopper 
and mix by inversion two or three times. Add 5 mL pyridine- 
barbituric acid reagent, dilute to volume with water, mix thor- 
oughly, and let stand exactly 8 min for color development. Meas- 
ure absorbance at 578 nm in a 10-mm cell using distilled water 
as a reference. Calculate slope and intercept of the curve. 

b. If sample pH is above 8, reduce it to 8.0 to 8.5 by careful 
addition of phosphate buffer. Measure 20 mL sample portion 
into 50-mL volumetric flask. If more than 0.20 mg CNC1-CN - / 
L is present use a smaller portion diluted to 20 mL with water. 
Add 1 mL phosphate buffer, stopper and mix by inversion one 
time. Let stand 2 min. Add 5 mL pyridine-barbituric acid re- 
agent, stopper and mix by inversion one time. Let color develop 

3 min, dilute to volume with water, mix thoroughly, and let stand 
an additional 5 min. Measure absorbance at 578 nm in 10-mm 
cell using distilled water as a reference. 



4-32 



INORGANIC NONMETALS (4000) 



5. Calculation 

Compute slope (m) and intercept (b) of standard curve as 
directed in 4500-CN-.E.5. 



50 



mL sample 



Cyanogen chloride as CN , mg/L = (ma ] + b) x 

where: 

a ] - absorbance of sample solution. 



6. Precision 1 

Cyanogen chloride is unstable and round-robin testing is not 
possible. Single-operator precision is as follows: 

Six operators made 70 duplicate analyses on samples of dif- 
ferent concentrations within the applicable range of the method. 



The overall single-operator precision within its designated range 
may be expressed as follows: 

log S„ - (0.5308 log c) - J. 9842 
log R - (0.5292 log c) - .1.8436 

where: 

c = mg CNCI-CN7L. 
S (1 - single-operator precision in the range of the method (precision 

is dependent on concentration), and 
R - range between duplicate determinations. 

The collaborative test data were obtained on reagent-grade 
water. For other matrices, these data may not apply. 

7. Reference 

1 . A M E R I C A N S OC I ET Y FOR Testi NG & M ATE R I A LS . 1989. R e se a rch Rep. 
D4165: 19-1 100. American Soc. Testing & Materials, Philadelphia, Pa. 



4500-CN" K. Spot Test for Sample Screening 



1. General Discussion 

The spot test procedure permits quick screening to establish 
whether more than 50 juug/L of cyanide amenable to chlorination 
is present. The test also establishes the presence or absence of 
cyanogen chloride (CNC1). With practice and dilution, the test 
reveals the approximate concentration range of these compounds 
by the color development compared with that of similarly treated 
standards. 

When chloramine-T is added to cyanides amenable to chlo- 
rination, CNCJ is formed. CNCl forms a red-blue color with the 
mixed reagent pyridine-barbituric acid. When testing for CNCl 
omit the chloramine-T addition. (Caution: CNCl is a toxic gas; 
avoid inhalation.) 

The presence of formaldehyde in excess of 0.5 mg/L interferes 
with the test. A spot test for the presence of aldehydes and a 
method for removal of this interference are given in Section 4500- 
CN-.B.3. 

Thiocyanate (SCN~) reacts with chloramine-T, thereby cre- 
ating a positive interference. The CN~ can be masked with form- 
aldehyde and the sample retested. This makes the spot test spe- 
cific for SCN ~ . In this manner it is possible to determine whether 
the spot discoloration is due to the presence of CN" , SCN", or 
both. 

2. Apparatus 

a. Porcelain spot plate with 6 to 12 cavities. 

b. Dropping pipets. 

c. Glass stirring rods. 

3. Reagents 

a. Chloramine-T solution: See Section 4500-CN \E.3#, 



b. Stock cyanide solution: See Section 4500-CN ".E. 36. 

c. Pyridine-barbituric acid reagent: See Section 4500-CN "\E. 3d. 

d. Hydrochloric acid, HCI, 1 4- 9. 

e. Phenolphthalein indicator aqueous solution. 

f. Sodium carbonate, Na 2 C0 3 , anhydrous. 

g. Formaldehyde, 37%, pharmaceutical grade. 



4. Procedure 

If the solution to be tested has a pH greater than 10, neutralize 
a 20- to 25-mL portion. Add about 250 mg Na 2 C0 3 and swirl to 
dissolve. Add 1 drop phenolphthalein indicator. Add 1 + 9 HCI 
dropwise with constant swirling until the solution becomes col- 
orless. Place 3 drops sample and 3 drops distilled water (for 
blanks) in separate cavities of the spot plate. To each cavity, add 
1 drop chloramine-T solution and mix with a clean stirring rod. 
Add 1 drop pyridine-barbituric acid solution to each cavity and 
again mix. After 1 min, the sample spot will turn pink to red if 
50 (xg/L or more of CN" are present. The blank spot will be 
faint yellow because of the color of the reagents. Until familiarity 
with the spot test is gained, use, in place of the water blank, a 
standard solution containing 50 \xg CN /L for color comparison. 
This standard can be made by diluting the stock cyanide solution 
(II 3b). 

If SCN is suspected, test a second sample pretreated as fol- 
lows: Heat a 20- to 25-mL sample in a water bath at 50°C; add 
0.1 mL formaldehyde and hold for 10 min. This treatment will 
mask up to 5 mg CN 7L, if present. Repeat spot testing pro- 
cedure. Color development indicates presence of SCN . Com- 
paring color intensity in the two spot tests is useful in judging 
relative concentration of CN and SCN - . If deep coloration is 
produced, serial dilution of sample and additional testing may 
allow closer approximation of the concentrations. 



CYANIDE (4500-CN )/Cynates 



4-33 



4500-CN- L. Cyanates 



1. General Discussion 

Cyanate (CNO~) may be of interest in analysis of industrial 
waste samples because the alkaline chlorination process used for 
the oxidation of cyanide yields cyanate in the second reaction. 

Cyanate is unstable at neutral or low pH; therefore, stabilize 
the sample as soon as collected by adding sodium hydroxide 
(NaOH) to pH > 12. Remove residual chlorine by adding sodium 
thiosulfate (Na 2 S 2 3 ) (see Section 4500-CN". B.2). 

a. Principle: Cyanate hydrolyzes to ammonia when heated at 
low pH, 

2NaCNO + H 2 S0 4 + 4H.O -» (NH 4 ) 2 SO, + 2NaHC0 3 

The ammonia concentration must be determined on one sample 
portion before acidification. The ammonia content before and 
after hydrolysis of cyanate may be measured by direct nessleri- 
zation (4500-NH V C), phenate (4500-NH v D), or ammonia- 
selective electrode (4500-NH 3 .F) method." The test is applicable 
to cyanate compounds in natural waters and industrial waste. 

b. Interferences: 

1) Organic nitrogenous compounds may hydrolyze to ammonia 
(NH 3 ) upon acidification. To minimize this interference, control 
acidification and heating closely. 

2) Metal compounds may precipitate or form colored com- 
plexes with nessler reagent. Adding Rochelle salt or EDTA in 
the determination of ammonia overcomes these interferences. 
Metal precipitates do not interfere with the ion-selective elec- 
trode method. 

3) Reduce oxidants that oxidize cyanate to carbon dioxide and 
nitrogen with Na 2 S 2 3 (see Section 4500-CN". G). 

4) Industrial waste containing organic material may contain 
unknown interferences. 

c. Detection limit: 1 to 2 mg CNO/L. 

2. Apparatus 

a. Expanded-scale pH meter or selective-ion meter. 

b. Ammonia-selective electrode. * 

c. Magnate mixer, with TFE-coated stirring bar. 

d. Heat barrier: Use a 3-mrn-thick insulator under beaker to 
insulate against heat produced by stirrer motor. 

3. Reagents 

a. Stock ammonium chloride solution: See Section 4500- 
NH,.C.3fif. 

b. Standard ammonium chloride solution: From the stock NH 4 C1 



* Orion Model 95-10, EIL Model 8002-2, Beckman Model 39565. or equivalent. 



solution prepare standard solutions containing 1.0, "10.0, and 
100. mg NH 3 -N/L by diluting with ammonia-free water. 

c. Sodium hydroxide, \0N: Dissolve 400 g NaOH in water and 
dilute to 1 L. 

d. Sulfuric acid solution, H 2 S0 4 , 1 + 1. 

e. Ammonium chloride solution: Dissolve 5.4 g NH 4 CI in dis- 
tilled water and dilute to 1 L. (Use only for soaking electrodes.) 

4. Procedure 

a. Calibration: Daily, calibrate the ammonia electrode as in 
45OO-NH3.F.4& and c using standard NH 4 C1 solutions. 

b. Treatment of sample: Dilute sample, if necessary, so that 
the CNO concentration is 1 to 200 mg/L or NH r N is 0.5 to 
100 mg/L. Take or prepare at least 200 mL. From this 200 mL, 
take a 100-mL portion and, following the calibration procedure, 
establish the potential (millivolts) developed from the sample. 
Check electrode reading with prepared standards and adjust in- 
strument calibration setting daily. Record NH 3 -N content of un- 
treated sample (B). 

Acidify 100 mL of prepared sample by adding 0.5 mL 1 + 1 
H 2 S0 4 to a pH of 2.0 to 2.5. Heat sample to 90 to 95°C and 
maintain temperature for 30 min. Cool to room temperature and 
restore to original volume by adding ammonia-free water. Pour 
into a 150-mL beaker, immerse electrode, start magnetic stirrer, 
then add 1 mL ION NaOH solution. With pH paper check that 
pH is greater than 11. If necessary, add more NaOH until pH 
11 is reached. 

After equilibrium has been reached (30 s) record the potential 
reading. Estimate NH 3 -N content from calibration curve. 

5. Calculations 

mg NH 3 -N derived from CNO ~/L - A - B 

where: 

A — mg NH.-N/L found in the acidified and heated sample portion 

and 
B = mg NH r N/L found in untreated portion. 

mg CNO-/L - 3.0 x (A - B) 

6. Precision 

No data on precision of this method are available. See 4500- 
NH3.A.4 for precision of ammonia-selective electrode method. 

7. Reference 

l. Thomas, R.F. & R.L. Booth. 1973. Selective electrode determina- 
tion of ammonia in water and wastes. Environ. Sci. Techno! . 7:523. 



4-34 



INORGANIC NONMETALS (4000) 



4500-CN- M. Thiocyanate 



1. General Discussion 

When wastewater containing thiocyanate (SCN " ) is chlorin- 
ated, highly toxic cyanogen chloride (CNCl) is formed. At an 
acidic pH, ferric ion (Fe 3+ ) and SCN™ form an intense red color 
suitable for colorimetric determination. 

a. Interference: 

1) Hexavalent chromium (Cr 6 ( ) interferes and is removed by 
adding ferrous sulfate (FeS0 4 ) after adjusting to pH 1 to 2 with 
nitric acid (HN0 3 ). Raising the pH to 9 with \N sodium hy- 
droxide (NaOH) precipitates Fe 3+ and Cr 3 *, which are then 
filtered out. 

2) Reducing agents that reduce Fe 3+ to Fe 2+ , thus preventing 
formation of ferric thiocyanate complex, are destroyed by adding 
a few drops of hydrogen peroxide (H 2 2 ). Avoid excess H 2 2 
to prevent reaction with SCN~. 

3) Industrial wastes may be highly colored or contain various 
interfering organic compounds. To eliminate these interfer- 
ences, 1 use the pretreatment procedure given in 11 Ac below. It 
is the analyst's responsibility to validate the method's applica- 
bility without pretreatment (H 4b), If in doubt, pretreat sample 
before proceeding with analysis (II 4c). 

4) If sample contains cyanide amenable to chlorination and 
would be preserved for the cyanide determination at a high pH, 
sulfide could interfere by converting cyanide to SCN"". To pre- 
serve SCN ~ and CN ~ , precipitate the sulfide by adding lead salts 
according to 4500-CN" .B.2 before adding alkali; filter to remove 
precipitate. 

5) Thiocyanate is biodegradable. Preserve samples at pH <2 
by adding mineral acid and refrigerate. 

6) If interferences from industrial wastes are not removed as 
directed in 11 4c below, consider adopting a solvent extraction 
technique with colorimetric or atomic absorption analysis of the 
extract. 2 - 3 

b. Application: 0.1 to 2.0 mg SCN"/L in natural or waste- 
waters. For higher concentrations, use a portion of diluted sam- 
ple. 

2. Apparatus 

a. Spectrophotometer or filter photometer, for use at 460 nm, 
providing a light path of 5 cm. 

b. Glass adsorption column: Use a 50-mL buret with a glass- 
wool plug, and pack with macroreticular resin (11 3/) approxi- 
mately 40 cm high. For convenience, apply a powder funnel of 
the same diameter as the buret to the top with a short piece of 
plastic tubing. 

3. Reagents 

a. Ferric nitrate solution: Dissolve 404 g Fe(N0 3 ) 3 -9H 2 in 
about 800 mL distilled water. Add 80 ml cone HN0 3 and dilute 
to 1 L. 

b. Nitric acid solution, 0.17V: Mix 6.4 mL cone HN0 3 in about 
800 mL distilled water and dilute to 1 L. 

c. Stock thiocyanate solution: Dissolve .1.673 g potassium thi- 
ocyanate (KSCN) in distilled water and dilute to 1000 mL; 1.00 
mL 1.00 mg SCN". 



d. Standard thiocyanate solution: Dilute 10 mL stock solution 
to 1 L with distilled water; 1.00 mL - 0.01 mg SCN". 

e. Sodium hydroxide solution, 4 g/L: Dissolve 4 g NaOH in 
about 800 mL distilled water and dilute to 1 L. 

/. Macroreticular resin, 18 to 50 mesh:* The available resin 
may not be purified. Some samples have shown contamination 
with waxes and oil, giving poor permeability and adsorption. 
Purify as follows: 

Place sufficient resin to fill the column or columns in a beaker 
and add 5 times the resin volume of acetone. Stir gently for 1 
h. Pour off fines and acetone from settled resin and add 5 times 
the resin volume of hexane. Stir for 1 h. Pour off fines and hexane 
and add 5 times the resin volume of methanol. Stir for 15 min. 
Pour off methanol and add 3 times the resin volume of 0.1/V 
NaOH. Stir for 15 min. Pour off NaOH solution and add 3 times 
the resin volume of 0.17V HN0 3 . Stir for 15 min. Pour off HN0 3 
solution and add 3 times the resin volume of distilled water. Stir 
for 15 min. Drain excess water and use purified resin to fill the 
column. Store excess purified resin after covering it with distilled 
water. Keep in a closed jar. 

g. Methyl alcohol. 

4. Procedure 

a. Preparation of calibration curve: Prepare a series of stand- 
ards containing from 0.02 mg to 0.40 mg SCN " by pipetting 
measured volumes of standard KSCN solution into 200-mL vol- 
umetric flasks and diluting with water. Mix well. Develop color 
according to H b below. Plot absorbance against SCN™ concen- 
tration expressed as mg/50 mL sample. The absorbance plot 
should be linear. 

b. Color development: Use a filtered sample or portion from 
a diluted solution so that the concentration of SCN"" is between 
0.1 and 2 mg/L. Adjust pH to 2 with cone HN0 3 added dropwise. 
Pipet 50-mL portion to a beaker, add 2.5 mL ferric nitrate, and 
mix. 

Fill a 5-cm absorption ceil and measure absorbance against a 
reagent blank at 460 nm or close to the maximum absorbance 
found with the instrument being used. Measure absorbance of 
the developed color against a reagent blank within 5 min from 
adding the reagent. (The color develops within 30 s and fades 
on standing in light.) 

c. Sample pretreatment: 

1) Color and various organic compounds interfere with ab- 
sorbance measurement. At pH 2, macroreticular resin removes 
these interfering materials by adsorption without affecting thi- 
ocyanate. 

2) To prepare the adsorption column, fill it with resin, rinse 
with 100 mL methanol, and follow by rinses with 100 mL 0.1/V 
NaOH, 100 mL 0.1/V HN0 3 , and finally with 100 mL distilled 
water. If previously purified resin is used, omit these preparatory 
steps, 

3) When washing, regenerating, or passing a sample through 
the column, as solution level approaches resin bed, add and drain 
five separate 5-mL volumes of solution or water (depending on 
which is used in next step) to approximate bed height. After last 



Amberlite® XAD-8. Rohm & Haas Company, or equivalent. 



CYANIDE (4500-CN-)/Thiocyanate 



4-35 



5-mL volume, fill column with remaining liquid. This procedure 
prevents undue mixing of solutions and helps void the column 
of the previous solution. 

4) Acidify 150 mL sample (or a dilution) to pH 2 by adding 
cone HN0 3 dropwise while stirring. Pass it through the column 
at a flow rate not to exceed 20 mL/min. If the resin becomes 
packed and the flow rate falls to 4 to 5 mL/min, use gentle 
pressure through a manually operated hand pump or squeeze 
bulb on the column. In this case, use a separator funnel for the 
liquid reservoir instead of the powder funnel. Alternatively use 
a vacuum bottle as a receiver and apply gentle vacuum. Do not 
let liquid level drop below the adsorbent in the column. 

5) When passing a sample through the column, measure 90 
mL of sample in a graduated cylinder, and from this use the five 
5-mL additions as directed in 11 3), then pour the remainder of 
the 90 mL into the column. Add rest of sample and collect 60 
mL eluate to be tested after the first 60 mL has passed through 
the column. 

6) Prepare a new calibration curve using standards prepared 
according to 11 4a, but acidify standards according to 11 4/>, and 
pass them through the adsorption column. Develop color and 
measure absorbance according to 11 Ab against a reagent blank 
prepared by passing acidified, distilled water through the ad- 
sorption column, 

7) Pipet 50 mL from the collected eluate to a beaker, add 2.5 
mL ferric nitrate solution, and mix. Measure absorbance ac- 
cording to II Ab against a reagent blank [see H 6) above]. 

8) From the measured absorbance value, determine thiocya- 
nate content of the sample or dilution using the absorbance plot. 

9) Each day the column is in use, test a mid-range standard 
to check absorption curve. 

10) Regenerate column between samples by rinsing with 100 
mL 0.1N NaOH; 50 mL 0.1 AT HN0 3 ; and 100 mL water. Insure 
that the water has rinsed empty glass section of the buret. Oc- 
casionally rinse with 100 mL methanol for complete regenera- 
tion. Adsorbed weak organic acids and thiocyanate residuals 
from earlier tests are eluted by the NaOH rinse. Leave the col- 
umn covered with the last rinse water for storage. 



6. Precision and Bias 4 

a. Precision: Based on the results of twelve operators in nine 
laboratories, at four levels of concentration, the precision of the 
test method within its designated range is linear with concentra- 
tion and may be expressed as follows: 



Reagent water; S, 



0.093* + 0.0426 
0.045* + 0.010 



Water matrix: S r = 0.055* + 0.0679 

S a = 0.024* + 0.182 

where: 

S T = overall precision, mg/L, 

S a = pooled single-operator precision, mg/L, and 

* = thiocyanate concentration, mg/L. 

b. Bias: Recoveries of known amounts of thiocyanate from 
Type II reagent water and selected water matrices including nat- 
ural waters, laboratory effluent, steel mill effluent, and dechlo- 
rinated and treated sanitary effluents were as follows: 





Added 


Recovered 








% 


Medium 


mg/L 


mg/L 


n 


S T 


Bias 


Bias 


Reagent 


1.42 


1.411 


30 


0.181 


-0.009 


-0.6 


water 


0.71 


0.683 


27 


0.091 


-0.027 


~4 




0.35 


0.329 


30 


0.084 


-0.021 


-6 




0.07 


0.068 


30 


0.052 


-0.002 


-3 


Selected 


1.42 


1.408 


26 


0.151 


-0.012 


-0.8 


water 


0.71 


0.668 


29 


0.096 


-0.042 


-6 


matrices 


0.35 


0.320 


29 


0.085 


-0.030 


-9 




0.07 


0.050 


29 


0.079 


-0.020 


-29 



For other matrices these data may not apply. 



7. References 



5. Calculation 

Compute slope (m) and intercept (b) of standard curve as 
directed in 4500-CN-.E. 5. 
Calculate thiocyanate concentration as follows: n ; 

mg SCN"/L = (ma, + b) x dilution factor 

where: 

a ) = absorbance of sample solution. 



4. 



Spencer, R.R., J. Leenheer & V.C. Marti. 1980. Automated col- 

orimetric determination of thiocyanate, thiosulfate and tetrathionate 

in water. 94th Annu. Meeting. Assoc. Official Agricultural Chemists, 

Washington, D.C. 1981. 

Danchick, R.S. & D.F. Bouz. 1968. Indirect spectrophotometry 

and atomic absorption spectrometric methods in determination of 

thiocyanate. Anal. Chem. 43:2215. 

Luthy, R.G. 1978. Manual of Methods: Preservation and Analysis 

of Coal Gasification Wastewaters. FE-2496-16, U.S. Dep. Energy, 

National Technical Information Serv., Springfield, Va. 

American Society for Testing & Materials. 1989. Research Rep. 

D4193: 19-1099. American Soc. Testing & Materials, Philadelphia, Pa.